The operational environment for a helicopter may include several different types of threats including but not limited to other aircraft, missiles and small arms fire. To operate and survive in this potentially hostile threat environment, many helicopters are equipped with a suite of advanced sensor systems. For example, many helicopters are equipped with electronic warfare (EW) equipment, such as electronic support measures (ESM) or Radar Warning Receiver (RWR) systems, which detect radio frequency (RF) signals emitted by other aircraft and ground-based systems, such as radars, and determine the characteristics of the detected RF signal (e.g., frequency, pulse repitition frequency (PRF), pulse width (PW), etc.). These EW systems may also determine the RF emitter type and operating mode of the RF emitter and also provide visual or aural alerts or warnings to the crew indicating whether the detected RF signal is associated with a potential threat to the helicopter. Many of these electronic warfare systems can also detect changes in the RF signal characteristics that indicate a change in the operating mode of the RF emitter, such as radar changing from a search mode to acquisition/targeting mode, indicating that a weapon launch is imminent.
Many helicopters are also equipped with one or more countermeasure systems, such as RF jamming systems. Installed RF jamming systems protect the helicopter from radar-guided weapons, by transmitting RF signals to disrupt the reception of the RF signal used for guidance, for example. Coordinating the transmission of RF jamming signals with helicopter maneuvers causes the radar guidance system of the approaching missile to lose its radar lock (e.g. radar track) on the helicopter causing the missile to miss the helicopter. RF jamming systems can also be used in conjunction with chaff and flare countermeasure systems.
Bullets from weapons pose a serious threat to helicopters because helicopters operate at low altitudes and frequently hover or fly at low speed, thereby creating targets within the range of many small arms weapons. The bullets fired by small arms, such as AK-47s, for example, and small projectiles fired from man portable weapons, such as RPGs, for example, can cause significant damage to helicopters, causing system failures and the loss of the helicopter and either killing or maiming the aircrew.
However, in many situations in the helicopter operating environment, small arms fire may be present that is directed at targets other than the helicopter, including weapons fired by friendly force or law enforcement personnel. These weapon firings pose no threat to the helicopter or aircrew. However, existing EW systems do not detect or provide any indications to the aircrew of the presence of small weapon-fired ballistic projectiles proximate to the helicopter.
Hostile Fire Indicating (HFI) systems have been recently added to the equipment installed on many helicopters. HFI systems detect the presence of weapons being fired in the vicinity of the aircraft. HFI systems detect the firing of bullets or small projectiles either with optical sensors that detect the muzzle flash associated with the firing of a weapon, or with acoustic pressure sensors, such as piezoelectric transducers that detect the disturbance in the atmosphere created by the shock wave generated by the bullet or small projectile moving through the air. However, HFI systems are strictly limited to detecting the presence of small arms firing activity in the vicinity of the helicopter and providing a bearing of the location of the detected small arms firing from the helicopter. HFI systems cannot determine if the detected small arms fire is directed at (i.e., targeting) the helicopter or is directed at another target.
With the existing onboard systems, the aircrew is frequently unaware of small arms fire that is directed at the helicopter. These projectiles may be passing close to or even hitting the aircraft with insufficient impact to be noticeable to the aircrew. As a result, helicopters have been returning from operations in dangerous environments with significant damage from small arms fired projectiles (e.g., bullets) with the aircrew unaware of their helicopter being targeted and damaged by the small arms fire.
A system that warns the aircrew when the small arms fire is targeting or being directed at the helicopter would significantly increase the survivability of the helicopter and aircrew in potentially hostile environments, including urban areas which provide many sheltered or concealed locations from which individuals can engage a helicopter in relative safety.
However, the space available for adding any new equipment to a helicopter that is not replacing an existing system is very limited and adding new equipment will increase cost of the helicopter, not to mention the weight, thereby limiting the effective flying range and payload of the helicopter. Additionally, since certain helicopter operations, such as combat search and rescue (CSAR), require helicopters to have significant range and endurance capabilities, increasing the weight of the helicopter may make the helicopter unsuitable for these types of operations. Therefore, adding additional equipment to existing aircraft systems to provide a bullet approach warning to the aircrew is not desirable due to the additional expense and negative impact on the range and payload capabilities of the helicopter, as well as the general lack of space within the helicopter.
Thus, what is needed is a system and method for warning the aircrew when ballistic projectiles, such as bullets from small arms weapons, are directed at the helicopter using existing sensors already installed on the helicopter.